You Can Take it With You: A Survey of Portable USB Headphone Amp/DACs

Introduction
I think portable amps/DACs and the hype that often surrounds them on message boards and review sites are a huge pain in the ass. Some of them are good, a lot of them suck. And as I've progressed through this hobby, I've strayed away from them.

But sometimes life happens. And you find yourself away from your home rig, or your home rig is gone, period...as is your home. And you need to listen to "Don't Think Twice" by Dylan over and over, but the soundcard in your laptop isn't cutting it even though your JH13s otherwise sound awesome. Or you find yourself without power or worse after a hurricane and the only thing that can ease your mind is some tunes from your battery-operated portable rig. Then you realize, yeah, portable amps/DACs have a place in this world because right now I could really use one.

And so life has happened to me over these last several months, and these are some of the portable amp/DACs Tyll boxed up and shipped over to me to listen to. I'm not going to get into every last detail of the tech and sound signature of these things. My goal here is just to communicate how well these things accomplish the elusive goal of rendering satisfying musical sound in a small package, especially at a given price. Because sometimes a portable amp is all you've got.

The devices surveyed in this article all share certain characteristics: they all are combined USB DACs and headphone amplifiers; I consider them all portable (some more than others); I used the JHAudio JH13 as my reference headphone; and none of them have ever been in my kitchen. From there, the feature sets vary widely; from the barest essentials to the ability to play hi-rez files to multiple gain settings. We'll focus on the shared features here.

thanks for giving the portable dac/amp its due... concerning the lack of volume pot, you fault the headstreamer for not having one, but applaud the dragonfly's design. why the change of heart? in a quotation from kevin at hrt, he explained the advantage. so is hrt's implamentation of not implamenting a volume control on the device equivolent to the dragonfly's implamentation? thanks

It's a fair point and a good catch. But I think what it comes down to is this: if there's room for a volume control on a device, I want it there. If there isn't room (as would seem to be the case on the DragonFly), then it is good to know that sufficient thought went into the implementation. But if I could change one thing about the DragonFly, it would be to have a volume control knob or button--or something--on board.

I don't like controlling the volume from my MacBook. Especially when using IEMs, there are times when I feel quick volume adjustments are needed. And maybe it's because of the Mac, or maybe it's because I'm spastic, but I prefer to have a volume control on the amp that I can quickly adjust rather than the buttons on the keyboard, which just aren't as easily responsive for me.

i agree, it is nice to have the control at your fingertips for adjusting the volume during those quiet passages (or those not-so-quiet quiet passages with compressed dynamic ranges). still, any idea how the impamentation differs between these two volume-potless amps?

i haven't yet read up on the dragonfly's implamentation. but here's what kevin stated elsewhere (pulled from headfonia comment section):

"The 'digitally controlled' part is a repurposing of the UI (user interface) of the host computer. We take over the system volume function and map it to the HeadStreamer's analog attenuator. This gives us multiple advantages over the other two types of volume controls that a product such as the HeadStreamer could use.

Compared to a digital attenuator, we don't sacrifice resolution by multiplying the sample by a value less than unity. This avoids the resolution loss that happens in any digital attenuator.

Compared to an analog volume control such as a potentiometer (POT), we don't have the inter channel mistracking that is common to all but very expensive (more than the retail cost of the HeadStreamer) implementation. We also have the convenience of a computer based UI so things like keyboard short cuts can be used.

We find our approach is the best of both worlds with the downsides of neither of the other approaches."

"While the digital domain is where your computer- based music experience starts, the analog domain requires attention too. Digital volume controls too often reduce signal resolution and decrease sound quality. Even when the iTunes volume slider is used, DragonFly’s high-resolution analog volume control carries out the instructions in the analog domain for the best sound quality. And DragonFly’s analog circuits are direct-coupled from the ESS converter chip’s output, avoiding the need for any extraneous, sonically degrading components in the signal path."

I'll check my notes to see if I have anything else that might shed some more light on this. But the basic gist seems to be the same.

Totally agree with the Bithead. It's very underrated. Sounds neutral to me, but perhaps not as much as their full sized Micro Amp. It's definitely not too warm or bassy because it sounds pretty impressive with even the HD-580 and 650. It doesn't really add any coloration of it's own. All my headroom amps have very smooth treble. At the same time I don't find them to be dark amps at all.

I kind of hate to admit this, but back when I was clueless I used the Airhead (same thing minus the DAC) with the K702 for years. The clipping light went off if cranked too loud, but it somehow sounded good. This was way back in 1962 before we had Line Out cables.

The only headphone the Airhead doesn't play well with I have is the K601. It'll even drive the 600 ohm Sextett, but the problem is not bad sound, but lack of volume! Who's crazy enough to use a 600ohm headphone with a portable amp...not me.

I've read the Bithead has slightly more roll off of the bass through USB rather than in amp only mode. Not sure if this is true or not.

Hopefully i'll find an upgrade to the Airhead that's just as portable (for use in a pocket etc) and can work well enough with the harder to drive headphones.

I'm using the BitHead with my HD 650, and it sounds fantastic. In high gain mode, it has plenty of headroom (heh), and while I don't doubt that there are amps out there that can drive the 650 better, to my ears, it's hard to beat the Bithead for the money.

One feature of the BitHead that only got a passing mention in the article but I think is worth making more note of is the crossfeed circuit. Crossfeed isn't necessary on most music, but I can't stand listening to music that has sounds hard-panned to one channel or the other through headphones without crossfeed enabled. If I ever get bit by the upgrade bug, I'd probably upgrade to one of HeadRoom's other amps (either the Micro stack or the Desktop amp), largely because they're among the few amps that have crossfeed built in. I know I can get a plugin for Foobar to handle it in software, but I like having the option to enable it system wide and not just in one program, and the simplicity of being able to just flip a switch to toggle it on/off.

work Dinny. I found the piece easy to read and digest and thought it hit the high points quite nicely. I also agree with you on the Bithead. Despite getting a bit long in the tooth it is still functionally a great bang-for-the-buck option in the portable DAC/Amp realm.

@ tdockweiler, if an amp is all you need I think I might have just the upgrade that you're looking for... but I'm not quite done with the article yet. Look for it in a few days if Tyll has time to publish before the CES madness hits.

I had these amps for quite some time and you'll notice that some are older models (though still hold their own with newer offerings). The absence of a piece of gear in this particular survey is no reflection, good or bad, on such gear. This is a crowded field and there are lots of worthy amps out there. I'm sure you'll see more on these pages.

I know, not exactly "Portable" per se...more "Transportable", but I'm still interested in knowing how the O2+ODAC Combo box holds up against any of these. Any chance of getting an actual review of it/them anytime soon?

it is nice to see the bithead included, as it really was/is 'early to the party' in the development of this now-crowded market. i had one for about four years. i then sold it. the design never bothered me, as some tend to dislike its finish. i sold it because i wanted to try other offerings. for all that time, it sufficed on my work desk, but i wanted a line out, better bit depth, optical in, etc, and i wanted to explore the other dacs and amps. even after moving on and trying others, i now realize that it was/is still stellar. i've seen some since i sold mine for < $100, and i think it is a steal. i'm always willing to recommend it, too.

Does anyone know of other contenders? Going up to $300 there are more, going with a 'wall wart' there are more, and no rca stereo outputs there are others (the Dragonfly will be first to mind) but givin the constraints I believe this is the list.

I would add two names to the list of strong contenders already tested: on the lower end of the price scale is the Fiio E10 which has a volume knob, defeatible bass boost, and a high/low gain switch and both a coaxial digital output and 1/8" analog output in addition to the headphone jack for around $55; the Audioengine D1 with a volume knob, a nice aluminum enclosure and a optical spdif input in addition to the usb input and output volume to spare for around $175.

It is unfortunately probably the fault of the volume pot. If you want to experiment with this try meansuring the imbalance at various pot settings. My suspicion is that you will find that it changes and probably gets better (more balanced) the futher into the pot range that you go. Make sure that you try this experiment on both gain settings.

If you do find that the imbalance is consistent throughout the volume pot range regardless of gain setting then it's likely that something is truly wrong with the circuitry and your only real course of action there would be to send it in for repair. Thankfully the folks at Headroom are as good as they come with issues like that in my experience.

I also agree that Headroom folks are very professional and among the best (I've meet Jorge and Headphone Samurai, and they both are great guys.) I had my BitHead for over half a year now, and I would rather like to fix the issue if it is something small.

I've been listening to music mainly through my Focusrite 2i2 and loaned UHA-6S so it's been a while since I give my BitHead a shot. In a quick listening test the imbalance is fairly obvious (tilted to the left channel.) None of that through the UHA-6S and 2i2.

Did a few measurements, and the difference between channels is actually in the range of 4-5 dB regardless of headphone output port, gain setting, and volume. As reference, the UHA-6S and 2i2 left and right channel imbalance measurements yield small fractions of a dB.

I seem to recall that HeadRoom changed something re the volume pot at some point in the Bithead's life to address some issue (not sure if it was hiss or imbalance or something else). I wonder if you have a pre-change model. Anyway, I always had great dealings with HR support, so I hope they get you sorted out.

I called HeadRoom yesterday and explained about the channel imbalance that I was experiensing.

Since I was using my BitHead through the USB port, I was adviced to give my BitHead a try using the line input instead, and was told that in some cases that solves the imbalance problem (could be some static charge build up somewhere in the circuit.) I was also reminded that if the problem persists, HeadRoom stands by their 2 year guarantee, and that I should give them a call back.

To test the line input I used the headphone out of my laptop (downloaded newer drivers and disabled some hard to get rid off "effects" in my HP laptop.) No balance issues I could easily pick, and measured less than 0.5 dB of channel imbalance. I then went back to using the USB input. Unfortunately the 4-5 dB channel imbalance was still there.

I originally thought this was a simple problem, but so far it seems I may need to send my BitHead for repairs.

When this things happen it becomes clear that having a company with an impecable costumer service and that fully backing up their products, such as HeadRoom, is important.

Just wanted to report back that I sent my Total BitHead for repairs and got it back today. My BitHead's 2 year warranty was honored and dealing with Mike was a pleasure.

The problem was a bad capacitor, probably close to the DAC IC (the venerable PCM2902 me thinks), which might explain why I had channel imbalance issues when using the usb port, but not when using the line input.

My BitHead is my first portable DAC/Amp, is very practical, sports two headphone outputs, crossfeed, IMO easy to use, and is backed up by a serious company. It is a no brainer... And it is on sale for $99 new.

Great article, but my purpose for a portable headphone amp would be to use it with my cellphone..Can any of these attached to your cellphone similiar to the FIIO which attaches with a provided strap. I like the meridian explorer and audioquest dragonfly but it seems as those would be left to dangle in my pocket and not actually attach to my cellphone.